The winding of a strand of parallel filaments onto a spool with the result that it is twisted as it is wound has presented a problem in the detection of that strand during the process.
Several prior art devices for strand detection are as shown in U.S. Pat. Nos. 4,074,871, 3,751,893, 3,840,869 and 3,734,422. U.S. Pat. Nos. 4,074,871 and 3,651,893 shows the disadvantage of the prior art this invention overcomes by allowing the filament to be maintained in a straight line from supply to take-up spool. U.S. Pat. No. 3,734,422 shows a tribo electric yarn monitor in contact with the filament. U.S. Pat. No. 3,840,869 shows a photoelectric transducer requiring the free path of the yarn be altered.
In the prior art, a sensor to detect the presence of the strand and to stop the winding machinery if the strand broke usually required a physical contact between the sensor and the strand. This physical contact at least distorted the free twisting path described from the supply package to the wound package and impeded the flow of the twist back to the supply package. Optical sensors did not provide a satisfactory solution since the narrow filament moved simultaneously about the spool in a direction transverse to the primary winding direction and required additional optical masks and lenses to form a directed light beam or to shape the perceived light beam. Other sensors required the strand path be distorted to lead the filament past a sensor altering the filament path from the supply to the winding spool. A guide for detecting a filamentary material is also disclosed in copending application Ser. No. 940,068 filed Sept. 7, 1978 and assigned to the common assignee. It discloses a guide and detector sensing the presence of a filament moving in a straight line.